VueJs The array change detection caveats
Introduction
When you try to set a value of an item at a particular index of an array initialized in the data option, vue can't detect the change and does not trigger an update to the state. In order to overcome this caveat you should either use vue's Vue.$set or use Array.prototype.splice method
Examples
Using Vue.$set
In your method or any lifecycle hook that changes the array item at particuar index
new Vue({
el: '#app',
data:{
myArr : ['apple', 'orange', 'banana', 'grapes']
},
methods:{
changeArrayItem: function(){
//this will not work
//myArr[2] = 'strawberry';
//Vue.$set(array, index, newValue)
this.$set(this.myArr, 2, 'strawberry');
}
}
})Using Array.prototype.splice
You can perform the same change instead of using Vue.$set by using the Array prototype'ssplice()
new Vue({
el: '#app',
data:{
myArr : ['apple', 'orange', 'banana', 'grapes']
},
methods:{
changeArrayItem: function(){
//this will not work
//myArr[2] = 'strawberry';
//Array.splice(index, 1, newValue)
this.myArr.splice(2, 1, 'strawberry');
}
}
})For nested array
If you have nested array, the following can be done
new Vue({
el: '#app',
data:{
myArr : [
['apple', 'banana'],
['grapes', 'orange']
]
},
methods:{
changeArrayItem: function(){
this.$set(this.myArr[1], 1, 'strawberry');
}
}
})Array of objects containing arrays
new Vue({
el: '#app',
data:{
myArr : [
{
name: 'object-1',
nestedArr: ['apple', 'banana']
},
{
name: 'object-2',
nestedArr: ['grapes', 'orange']
}
]
},
methods:{
changeArrayItem: function(){
this.$set(this.myArr[1].nestedArr, 1, 'strawberry');
}
}
})